There have been known epoxy-amine adducts formed by a reaction between an amine compound and an epoxy compound. Such epoxy-amine adducts are also called “amine adducts.” As examples of the amine adducts, Patent Literature (PTL) 1 and PTL 2 disclose addition compounds each obtained by allowing a glycidyl-containing epoxy resin to react with a dialkylamine; and powders of the addition compounds whose surface is neutralized with an acidic substance. PTL 3 discloses an epoxy-amine adduct that is obtained by a reaction typically of an amino compound having an amino group and an N,N-dialkylamino group with an epoxy resin having more than one glycidyl group on average per molecule in a specific ratio.
The amine adducts are used as curing agents (latent curing agents) for epoxy resins, as disclosed in PTL 1 to 3. In addition to the curing agent use, the amine adducts have recently been used typically as adhesion improvers that are used in composite materials (fiber-reinforced composite materials) including a reinforcing fiber and a resin for better adhesion between the resin and the reinforcing fiber. The reinforcing fiber is exemplified by carbon fibers.
Separately, carbon-fiber-reinforced composite materials have very excellent heat resistance and mechanical properties and have been increasingly used in various uses. The carbon-fiber-reinforced composite materials are fiber-reinforced composite materials as composite materials of a carbon fiber and a resin, where the carbon fiber has a specific strength, a specific modulus, and heat resistance at high levels and is lightweight. The carbon-fiber composite materials generally employ sizing agents (binders). The sizing agents are exemplified by bisphenol-A diglycidyl ether (see PTL 4 and 5), poly(alkylene oxide) adducts of bisphenol-A (see PTL 6 and 7), poly(alkylene oxide) adducts of bisphenol-A to which epoxy group is added (see PTL 8 and 9), and epoxy adducts of polyalkylene glycols (see PTL 10 to 12). The sizing agents are applied as a paste or sizing material to a carbon fiber so as to improve workability in higher-order processing of the carbon fiber that has poor compactness.